1. Field of the Invention
The present invention relates to an array antenna on which a plurality of antenna elements for radiating radio waves are arranged generally in line, forming a linear array.
2. Description of the Related Art
There exist various kinds of conventionally known array antennas employing a configuration in which a plurality of antenna elements are formed on a substrate and the individual antenna elements are connected to secondary feeder lines which are arranged parallel to one another.
FIG. 6 is a plan view generally showing the configuration of a conventional array antenna on which a plurality of antenna elements are arranged generally in line. This kind of conventional array antenna is shown in Japanese Patent Application Publication No. 1999-312909, in which antenna elements are arranged side by side as shown in FIG. 6.
Referring to FIG. 6, the array antenna includes a substrate 1 having a rectangular shape in plan view, multiple antenna elements 2a–2i formed on a surface of the substrate 1, secondary feeder lines 3a–3i connected respectively to the antenna elements 2a–2i, a primary feeder line 4 connected to the individual secondary feeder lines 3a–3i, and an outgoing line 5 of which one end is connected to the primary feeder line 4 and the other end is connected to an external circuit (not shown). The substrate 1 is made of a dielectric material while the antenna elements 2a–2i, the secondary feeder lines 3a–3i, the primary feeder line 4 and the outgoing line 5 are made of a patterned conductor layer formed on the surface of the substrate 1.
More specifically, the antenna elements 2a–2i are arranged on the substrate 1 generally in line along a longitudinal (horizontal as illustrated in FIG. 6) axis of the substrate 1 at specified equal intervals with long sides of the successive antenna elements 2a–2i placed side by side. The secondary feeder lines 3a–3i are connected to the respective antenna elements 2a–2i on the sides thereof (right sides as illustrated in FIG. 6) which are perpendicular to and face one direction along the longitudinal axis of the substrate 1. This arrangement is used to ensure that the antenna elements 2a–2i produce electric fields in the same direction and the individual secondary feeder lines 3a–3i have a specific impedance. The interval between the successive antenna elements 2a–2i is normally made equal to an integer multiple of the wavelength of radio waves such that the radio waves emitted from the antenna elements 2a–2i are synchronized in phase and radiation pattern of the array antenna is optimized.
In the aforementioned configuration, all of the antenna elements 2a–2i are arranged at regular intervals, whereby the array antenna radiates a high-intensity radio wave in a specified direction.
As shown in FIG. 6, the substrate 1 has an overall length Lpwb and the array antenna has a substantial antenna length Lant. In the aforementioned conventional array antenna, the secondary feeder lines 3a–3i are connected to the antenna elements 2a–2i on the sides thereof facing the same direction along the longitudinal axis of the substrate 1. It is therefore impossible to form antenna elements all the way from the proximity of one end of the substrate 1 to the proximity of the other end of the substrate 1 along the longitudinal axis thereof. As a result, the substantial antenna length Lant is shorter than the overall length Lpwb of the substrate 1, making it impossible to form the array antenna on the substrate 1 in an efficient fashion.